High Speed Analysis of Anionic Surfactants

Significance of the Topic

Anionic surfactants are widely used in household and industrial detergents and can persist in water sources, posing ecological and health risks. Reliable monitoring of these compounds is essential for meeting regulatory standards and ensuring safe drinking water. High-performance liquid chromatography (HPLC) methods that deliver both sensitivity and speed are critical for routine water quality testing and environmental monitoring.

Objectives and Study Overview

This study aimed to evaluate high-speed HPLC methods for quantifying anionic surfactants (carbon chain lengths C10–C14) in tap water. The performance of three octadecyl-bonded silica columns was compared: Shim-pack VP-ODS (5 µm), Shim-pack FC-ODS (3 µm) and Shim-pack XR-ODS (2.2 µm). Key goals included reducing analysis time while maintaining compliance with the Japanese Ministry of Health, Labour and Welfare reference method.

Methodology

Tap water samples were concentrated 250-fold by solid phase extraction according to the official water quality inspection procedure. A standard mixture of C10–C14 surfactants (1 mg/mL each) was diluted to provide calibration levels equivalent to 0.002–0.04 mg/L in sample water. Separation was achieved using gradient or isocratic elution with a water/acetonitrile (35/65, v/v) mobile phase containing 0.1 mol/L sodium perchlorate.

Used Instrumentation

• Chromatograph: Shimadzu Prominence-i integrated HPLC system
• Fluorescence detector: RF-20A (Ex 221 nm, Em 284 nm)
• Columns:
  • Shim-pack VP-ODS: 150 × 4.6 mm, 5 µm
  • Shim-pack FC-ODS: 150 × 4.6 mm, 3 µm
  • Shim-pack XR-ODS: 100 × 3.0 mm, 2.2 µm
• Flow rates: 1.0 mL/min (FC-ODS), 0.7 mL/min (XR-ODS)
• Column temperature: 40 °C
• Injection volume: 20 µL (FC-ODS), 5 µL (XR-ODS)

Main Results and Discussion

• Chromatographic separation by carbon number was achieved on all three columns.
• FC-ODS reduced total elution time from ~20 min (VP-ODS) to ~10 min while preserving peak resolution.
• XR-ODS further shortened analysis to ~5 min without loss of separation.
• Calibration curves for C10–C14 showed excellent linearity (R2 ≥ 0.9999) across 0.5–10 mg/L standards.
• Relative errors at all concentration levels were ≤ 10 % and repeatability (RSD) for six replicates was ≤ 1 % for both columns.

Benefits and Practical Applications

• Significantly higher sample throughput supports routine monitoring and quality control in water analysis laboratories.
• Maintained compliance with national regulatory requirements for anionic surfactant quantification.
• Reduced solvent and buffer consumption due to shorter run times, lowering operational costs.
• Flexible adoption in existing HPLC setups without major equipment modifications.

Future Trends and Potential Applications

Emerging directions include coupling ultra-high-pressure liquid chromatography (UHPLC) with mass spectrometry for enhanced selectivity and lower detection limits. Automation of sample preparation and online SPE integration may further improve laboratory efficiency. Application of similar high-speed methods to other surfactant classes and environmental analytes can broaden monitoring capabilities.

Conclusion

The study demonstrates that small-particle ODS columns (FC-ODS and XR-ODS) enable rapid, accurate and reproducible quantification of anionic surfactants in water. The XR-ODS column in particular achieves a fourfold reduction in analysis time compared to conventional columns, supporting high-throughput compliance with water quality standards.

Reference

1. Ordinance No. 101 of the Ministry of Health, Labour and Welfare, Japan (MHLW), May 30, 2003; partially revised March 2, 2015.
2. Ordinance No. 261 of the Ministry of Health, Labour and Welfare, Japan (MHLW), July 22, 2003; partially revised March 28, 2018.